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Unified Diff: third_party/WebKit/Source/core/layout/ng/ng_column_mapper.h

Issue 2632523002: [LayoutNG] Initial support for multicol, introducing NGBlockBreakToken. (Closed)
Patch Set: Add TODO. Created 3 years, 11 months ago
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Index: third_party/WebKit/Source/core/layout/ng/ng_column_mapper.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_column_mapper.h b/third_party/WebKit/Source/core/layout/ng/ng_column_mapper.h
new file mode 100644
index 0000000000000000000000000000000000000000..b4ab09f918c4ee7ce7c22075180d1b81a8cfd928
--- /dev/null
+++ b/third_party/WebKit/Source/core/layout/ng/ng_column_mapper.h
@@ -0,0 +1,82 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NGColumnMapper_h
+#define NGColumnMapper_h
+
+#include "core/CoreExport.h"
+#include "core/layout/ng/ng_block_break_token.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+// Keeps track of the current column, and is used to map offsets from the
+// coordinate established by the fragmented flow [1] to visual coordinates.
+//
+// [1] https://drafts.csswg.org/css-break/#fragmented-flow
+//
+// TODO(mstensho): Add a NGFragmentainerMapper super class. There are other
+// fragmentation types than multicol (regions, pagination for printing).
+class CORE_EXPORT NGColumnMapper
+ : public GarbageCollectedFinalized<NGColumnMapper> {
+ public:
+ NGColumnMapper(LayoutUnit inline_progression, LayoutUnit block_size)
+ : inline_progression_(inline_progression), block_size_(block_size) {}
+
+ // Column block length.
+ LayoutUnit BlockSize() const { return block_size_; }
+
+ // Offset for next break, in the fragmented flow coordinate space.
+ LayoutUnit NextBreakOffset() const {
+ return last_break_block_offset_ + block_size_;
+ }
+
+ // Convert an offset in the fragmented flow coordinate space to the visual
+ // coordinate space.
+ void ToVisualOffset(NGLogicalOffset& offset) {
+ offset.inline_offset += inline_offset_;
+ offset.block_offset -= last_break_block_offset_;
+ }
+
+ // Specify where in the content to start layout of the next column.
+ void SetBreakToken(NGBlockBreakToken* token) {
+ DCHECK(!break_token_);
+ break_token_ = token;
+ }
+ bool HasBreakToken() const { return break_token_; }
+
+ // Advance to the next column. Returns the break token to resume at. If
+ // nullptr is returned, there's no more content to process.
+ NGBlockBreakToken* Advance() {
+ NGBlockBreakToken* token = break_token_;
+ break_token_ = nullptr;
+ if (token) {
+ inline_offset_ += inline_progression_;
+ last_break_block_offset_ += block_size_;
+ }
+ return token;
+ }
+
+ DEFINE_INLINE_TRACE() { visitor->trace(break_token_); }
+
+ private:
+ // Where to resume in the next column.
+ Member<NGBlockBreakToken> break_token_;
+
+ // The sum of used column-width and column_gap.
+ LayoutUnit inline_progression_;
+
+ // Inline offset to the current column.
+ LayoutUnit inline_offset_;
+
+ // Block size of a column.
+ LayoutUnit block_size_;
+
+ // Amount of content held by previous columns.
+ LayoutUnit last_break_block_offset_;
+};
+
+} // namespace blink
+
+#endif // NGColumnMapper_h

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